Common Shares (Narrative) (Details) - USD ($) $ in Millions	1 Months Ended		3 Months Ended		6 Months Ended
	Jul. 31, 2015	Nov. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Dec. 31, 2014
Number of common and preferred stock authorized to issue			185,000,000		185,000,000
Common shares, authorized			175,000,000		175,000,000		175,000,000
Preferred shares, authorized			10,000,000		10,000,000
Common Stock, Shares, Outstanding			86,900,000		86,900,000
Preferred Stock, Shares Outstanding			0		0
2014 ATM program [Member]
Maximum aggregate offering price of common shares		$ 331.3
Stock Issued During Period, Shares, New Issues			0	0	0.0	0.0
Subsequent Event [Member] | 2014 ATM program [Member]
Stock Issued During Period, Shares, New Issues	0
Maximum aggregate offering price of remaining common shares available for sale	$ 315.3
Line of Credit [Member]
Line of Credit Facility, Current Borrowing Capacity			$ 500.0		$ 500.0